I don't have two, but could it be that you have more than one phone (i.e. wife, girlfriend, other's??) paired in each head unit. I have my phone paired to my 2013 and my wife's 2013 GTI. If her phone is near by (within 30-40 feet) when I drive the GTI(grocery getter) her phone will take precedence and my phone won't connect.
Not saying that is it, but the first time I experienced this I was like "WTF?."